I’m in the final couple weeks of a large renovation which included creating a new master bath and walk-in closet for our “master suite” on the 2nd floor and a new guest bath on the same floor. This was a fairly large project involving removing the original bathroom and converting that into a pass-thru walk-in closet off the master bedroom to a new master bath. A second guest bath was also added on the 2nd floor. Doorways had to be removed, new entry ways had to be added, and new interior walls built. For both bathrooms there was no existing plumbing that could be re-used so all new plumbing. All new electrical wiring and an upgrade to our electrical panels also was required. All this in a historic home that was built around 1883. 
Some key features to give you an understanding of the scope:
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[li]Walk-in closet with custom built-in cabinetry on both sides.[/li][li]Master Bath with water closet, 7x4 shower with marble walls and shower heads on each side, and a frameless glass entry, free-standing tub (Bain Ultra), double vanity, and marble floors extending through the master bathroom and the walk-in closet.[/li][li]Guest Bath with vanity/sink, shower/tub combo, toilet, and washer/dryer (2nd floor laundry).[/li]Total square footage impacted is about 750 square feet of a 1500 square foot 2nd floor.
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We are now in week 16 of what was originally planned as an 8 week project. We are using a local home renovation company for all of the work - soup to nuts they do it all.
We started with an architect to create drawings of the existing space and then based upon our wants/needs/must-haves he created several floor plan layouts for us to review. From these we selected the layout we liked the best. The architect then created additional drawings showing electrical, plumbing, etc. We lucked out in that we have a friend who is an architect and agreed to do this as a side-job for a reasonably low fee. Hiring an actual architectural firm would have cost us thousands more.
With the architect plans, we then engaged with about 10 different contractors/renovation firms to solicit bids. We located these providers in a variety of ways; referrals from friends, Google searches, driving around neighborhoods where gentrification and renovation is common and looking for yard signs of contractors, etc. We had a pretty big range of bids ($40K to $150K) and I have to say that in hindsight the low bids were nowhere near realistic. We also requested and checked references for each contractor that we considered a possiblity. At the end of the day we selected the contractor that we felt was best able to handle a job of this size and whose estimate seemed to be at least grounded in reality. Once selected, we signed a fixed-bid contract and the work began. The contractor is responsible for all work defined in the contract, obtaining permits, and scheduling appropriate inspections (framing, insulation, electrical, plumbing, etc.)
We never had a designer per se. We do have a friend who is an interior designer and we would run a few ideas by him for input that helped. But for the most part we designed everything ourselves from selecting the tile, designing the custom cabinetry, wall paint colors, fixtures, etc. It sucked, it was daunting, and we felt very out of our element even with some occasional assistance from our designer friend. We did a lot of online research looking at images of bathrooms and closets to find ideas we liked and wanted to incorporate. For the closet cabinetry we actually scheduled a meeting with a national company and their designer came up with our a plan including specification/drawings. Of course we didn’t use them for the final product but it gave us what we needed to show our cabinet maker what we were thinking. In hindsight we made some small design mistakes that although correctable are also something we ca live with. I would have much preferred it to be like I see on t.v., a designer with a gee-whiz iPad app shows me a 3-d rendering of what they propose and I agree and by the end of the 2nd commercial break everything is done!
What to expect… well, expect the project to run a lot longer than originally quoted. If it stays on target then great but that certainly does not seem to be the norm. I would also look for a fixed bid and get them to detail EVERYTHING in EXCRUCIATING detail in their bid. Each line item of work to be done with the associated cost.
Expect that once hammers start hitting walls you’ll discover complications that will add costs and time to the project. We found a structural issue that had to be addressed that added a couple thousand dollars. We also had scope creep, things that we didn’t think about when looking at paper or thought were really good may not translate to reality well. So expect changes had to be made out of necessity or because you changed your mind and wanted to do tweak something differently.
Expect to live in a mess for awhile. Our work crew have been awesome about containing demo/construction mess but no matter how much they do there will still be a mess.
Expect frustrations! Extra costs, extra time, unforeseen complications and complications caused by incompetence (we have had the worst plumber in history on this job!), things done wrong that have to be redone (again, the plumber). “Things” happen and keeping a level head and being firm in what you want will be needed. And sometimes you just have to be the use the “Bitch Homeowner” card to get things done.
…and hopefully as you near the end of the project you can expect to be excited to see what started as a vision in your head of what you want become tangible and real. I walk through all the new spaces several times a day just looking at stuff and seeing how it is coming together and it makes me feel really good. And my wife cannot wait to use her new free standing soaker tub or for us to be able to shower together without bumping into each other constantly.